This invention concerns adjusting the tracking of a magnetic tape digital video recording and reproducing equipment of the kind having a rotary multiple-head device for obliquely scanning a lengthwise-moving magnetic tape, which equipment also includes a servo control system controlling the speed of lengthwise motion of the tape by reference to a manually variable electrical reference signal and a signal derived from motion of the tape and also includes a manual tracking adjustment means and apparatus for correction and/or concealment of errors.
A book by Friedrich Manz, "Videorecorder-Technik" published by Vogel-Verlag/Wurzburg, 1979 pgs. 78-82, describes the recording of video signals on magnetic tape, the rotating heads of a scanning device and the playback of such signals from the magnetic tape with the same device. A servo unit or system controls the tendency of the tape transport speed to fluctuate. By intervening in the phasing of the servo it is possible to correct tracking errors with a tracking adjustment knob. The tracking adjustment knob is to be adjusted so that a television picture of the reproduced video signal, used for an adjustment criterion during the adjustment procedure will have the least possible disturbances. In magnetic tape equipment for recording and reproducing digital video signals there are usually provided circuits for error correction and error concealment in the playback portion of the equipment, which correct erroneous data in the reproduced video signal and conceal uncorrectible errors. When a tracking adjustment is made these digital circuit devices prevent obtaining any sensitive evaluation of the disturbances in the television picture. It is in fact impossible to determine optically whether the magnetic heads of the scanning device are centered on the recorded tracks which they are reading.